U.S. Pat. No. 3,938,741 issued to Allison shows and describes a thermal shutoff valve for a shower in which a sensing element in the flow path moves a closure disc against the seat. Allison stresses the feature that the dynamic water pressure assists in achieving a rapid closure. A small bypass produces a harmless stream. Adjustment of control valves results in the sensing element reversing the force on the closure disc. However, the very forces that assisted in achieving a rapid closure of the valve operated to impede the rapid reset of the mechanism. Thus, the water pressure on the closure is a significant force to overcome. The return spring must overcome this pressure as well as the friction of the power element. The reset time accordingly varies widely.
U.S. Pat. No. 1,877,510 to Hughes shows an antiscald device in which the sensing element is downstream of the control valve. The sensing element is therefore not intimately associated with the reduced flow of water in the near shutoff position. This results in a very slow reset time. The primary object of the present invention is to provide a thermal shutoff valve that restricts flow within a very short period of time following rise in water temperature above a critical level, and that very promptly resets the shutoff valve for full normal operation following reduction of temperature below the critical point. A five second period is rapid for shutoff; a twenty second period is prompt for reset.